Viruses are everywhere. Scientists estimate the number of viruses to be in the range of 10,000,000,000,000,000,000,000,000,000,000 – if stacked on top of each other, the teeny things would reach out into space to a height of 200 million light-years. That’s a lot of viruses.

But biologists at San Diego State University recently stumbled across a novel virus that is far more unique than many of the other viruses we know about. The researchers found that the new guy, named crAssphage, is present in more than half the world’s population. It infects one of the most common types of gut bacteria, Bacteroidetes, the phylum of bacteria believed to be linked with obesity, diabetes and other gut-related diseases.

Robert A. Edwards, a bioinformatics professor at SDSU, and his colleagues came across the new virus by accident when screening previous studies in a hunt for new viruses.

Looking through fecal specimens, they noticed a particular cluster of viral DNA that a number of samples had in common. When the team checked a comprehensive listing of known viruses, they couldn’t find it. They next looked for the virus in the database of the National Institute of Health’s Human Microbiome Project and Argonne National Laboratory's MG-RAST database; there they found the virus in an abundance human feces samples.

They determined that not only was this a previously undiscovered virus, but that 50 to 75 percent of the world's population plays host to it.

“It’s not unusual to go looking for a novel virus and find one,” Edwards said. “But it’s very unusual to find one that so many people have in common. The fact that it’s flown under the radar for so long is very strange.”

And just how far-flung is the virus? The team found the virus in people across the United States, Europe, Korea and Japan. "But we think the virus is likely found worldwide," Edwards told NPR. "We've basically found it in every population we've looked at. If we tested Africans, we think we'd find it in them, too."

The researchers note that since it’s so widespread, it’s probably an old virus. Edwards said that as far as they can tell, it’s as old as humans are. The researchers are not sure how the virus is transmitted, but since it’s not found in infants, it is assumed that it is not passed on by the mother, but is acquired during childhood.

And if you’re starting to feel a bit of panic about a virus that is quite likely residing in your gut right this very minute, there’s no cause for alarm. CrAssphage doesn’t make people sick. That said, it may play a role in obesity and diabetes.

As noted before, the virus takes up residence in Bacteroidetes. NPR compares the system to a Russian nesting doll: “the virus lives inside the bacterium, which lives inside our gut.” (A microscopic turducken also comes to mind.) Bacteriodetes are suspected of being star players in the link between gut bacteria and obesity.

Once the virus is isolated, Edwards hopes to explore its role in obesity. It’s possible the virus somehow affects the activity of Bacteroidetes colonies, but whether crAssphage promotes or suppresses obesity-related processes in the gut is still unknown. The virus could also potentially be used to prevent or have an impact on other gut-related diseases. Once the virus and its relationship to the gut are better understood, Edwards envisions the potential for custom medicines based on this virus.

“This could be a key to personalized phage medicine,” he said. “In individuals, we could isolate your particular strain of the virus, manipulate it to target harmful bacteria, then give it back to you.”

And about that curious moniker? As much as it may sound like it, there was no bathroom humor employed when naming the virus. The "crAss," comes from the computational tool – Cross Assembly – that the researchers used to find the virus; "phage" comes from the name of viruses that infect bacteria. When NPR pointed out that the name brings to mind where the team found the virus, Edwards said with a chuckle, "Oh, no, we never thought of that. We would never be crass." (Or did he mean crAss?)

Watch Edwards talk about the newest virus on the block in the video below: